19 October 2018 Human neurons are much larger than in mice and rats of model organisms, so it has been…
Human neurons are much larger than in mice and rats of model organisms, so it has been unclear if it is size that makes a difference in our brain’s computational power. Now, in a study published in October 18 in the journal Cell researchers show that the human neurons, unlike other animals, use highly-allocated signaling. Human dendrites – the tree-like branch structures that act as neurons’ antennas ̵
1; process electrical signals differently than dendrites in rodents, the most common model systems for studying neuronal properties.
“Human neurons are, in principle, a rotten neuron, but since it is so much longer, the signals have a lot longer to travel. Human dendrites thus have another input function” from rats, says senior writer Mark Harnett, Fred and Carole Middleton Career Development Assistant Professor of the Department of Brain and Cognitive Sciences at the Massachusetts Institute of Technology. “Dendrites further away from the cell body have fewer ion channels, which control signal processing. That was something we definitely did not expect.”
Harnett, who studies how neurons’ biophysical properties shape brain information information, believes that our longer, larger dendritic arbors convey human neurons and their respective circuits with improved computational ability.
“Human neurons are more electrically divided and can use this,” he says. “We believe that with low ionic density at the ends of dendrites, the cell may have as many sub-bodies as possible. The longer the branches are, the more independent entities. You have many more devices to calculate within a single neuron.”  “Integrating different information streams in this way could give individual neurons the reliability of small computing networks,” says Harnett.
Using a technique called patch-clamp recording, where small glass pins are sealed against the cell membrane to measure detailed electrical properties, the researchers recorded for the first time direct dendritic activity in human living brain tissue. The human tissue (from brain surgery) was obtained from the epilepsy patients’ temporal lobe.
Finally, work may favor patients with epilepsy, where small parts of brain tissue are sometimes removed to control non-medicated seizures. “People have used animal models to think about epilepsy for a long time, but there are clear differences, at least in dendrites, between people and rodents,” says Harnett. “The better we understand the ducts and membrane upturn, the more insight we get into the epilepsy mechanisms and how to treat it.”
The next step also involves determining the relationship between neuronal size and electrical properties of other species in order to gain insight into the development of the cortex.